javascript中闭包的真正作用

function Person(name) {
var _age;
function setAge(n) {
_age = n;
}
function getAge() {
return _age;
}

return {
name: name,
getAge: getAge,
setAge: setAge
};
}

var p1 = person('张三');
p1.setAge(25);
p1.getAge() // 25

function createIncrementor(start) {
return function () {
return start++;
};
}

var inc = createIncrementor(5);

inc() // 5
inc() // 6
inc() // 7